Process of producing sintered metal sheets



H. I. RAIKLEN PROCESS OF PRODUCING SINTERED METAL .SHEETS Aug. 18, 1959 Filed oct. 13. 1954 Patented Aug. 18, 1959 rRoCEss oF rRoDUCiNo SINTERED METAL smears Hyman l. Raiklen, Flushing, N Y., assignor, by mesne assignments, to Sylvania Electric Products lne., Wilmington, Del., a corporation of Delaware Application @ctober 13, 1954, Serial No. 462,083

3 Claims. (Cl. 75-2`14) The present invention relates to a method of manufacturing powdered metal sheets, and in particular is concerned with a continuous process for the rolling of non-compacted powdered metal into thin sintered sheets.

In the eld of powdered metallurgy, it is known to roll metallic powders into a thin sheet or strip by feeding the metallic powder into a rolling mill, either vertically or horizontally. Following rolling, the metallic powder is compacted into a densified sheet or strip having sufficient green strength and rigidity to be self-supporting, which strip may be sintered in an appropriate non-oxidizing atmosphere, such as hydrogen or nitrogen. The compacted and sintered strip may be then further processed in accordance with well understood metallurgical techniques, such as by re-rolling and annealing, to produce metallic sheets of required density and strength.

For rolling mills having a Vertical feed, precautions must be taken to achieve proper feed of the metallic powder to the rolling mill. Further such vertical feed requires reorientation of the rolls and mechanism of the conventional horizontally-fed rolling mill and fairly elaborate mechanisms to obtain delivery of powder to the mill for compacting into a green sheet. Still further, subsequent treatment, such as sintering, re-rolling and annealing, usually requires a change of direction of the compacted green sheet, with possible risk of fracture or bending of the green sheet.

Mills which employ horizontal feed or delivery of the powdered material usually incorporate a metal conveyor or metal carrier which extends between the rolls of the mill for introducing the metallic powder to the rolls. It has been found that such conveyor or carrier should be smooth and free from irregularities, and should be sufficiently hard to resist deformation as it passes through one or more pairs of rolls of the mill. A tempered steel has been found to possess the several properties for such carrier or conveyor. When using such tempered steel conveyors, it is frequently necessary to take precautions to avoid adherence of the compacted metal sheet to the conveyor proper. In this connection it is known in the art to employ a revolving brush which continuously cleans the surface of the metal conveyor and dusts` the same with graphite or other material appropriate to prevent adherence of the powdered metal to the conveyor.

It is an object of the present invention to provide an improved method of forming sheets by powdered metallurgy techniques which obviates one or more of the aforesaid diiculties. Specifically it is within the contemplation of the present invention to provide an improved process for forming sheets or strips from metallic powders in which the several processing steps occur during feed of the powdered material to the rolls in a substantially horizontal plane. To advantage such horizontal feed of the powdered metal is highly compatible with known equipment for rolling, sintering, re-rolling and annealing of powdered metallic materials.

It is a still further object of the present invention to provide an improved process for continuously fabricating thin sheets by powdered metallurgy techniques which minimizes the risk of introducing harmful stresses into the sheets during processing. Specifically the possibility of introducing stresses during processing and/or fracture or bending of a partially processed strip is substantially overcome by a process in which the non-compacted metallic mass of powder, the compacted sheet, and the sintered sheet is fed in a substantially continuous and horizontally extending feed path or plane.

In accordance with aspects of the present invention, a thin strip of metal is formed by applying a loose layer of metal powder on a horizontally-extending, heatdestroyable conveyor, carrier or base, feeding the conveyor supporting the loose layer of metal horizontally through a rolling mill to compact the loose layer of metal powder into a green sheet or strip, which is usually of suliicient density to be self-supporting, and thereafter sintering the green sheet or strip. Sintering causes the loose metallic particles to cohere thus making the sheet self-sustaining; at the same time sintering substantially destroys the conveyor which has lost its usefulness and as such is expendable.

Among the materials found suitable for the heatdestroyable or expendable conveyor are organic or cellulosic materials which are gasifiable or burn on being subjected to heat such as is encountered in sintering most metal powders. Paper of a composition leaving a low ash residue has been found suitable in supporting the powder for delivery to the rolling mill; the paper is substantially removed during the heating, and if necessary residues may be removed by directing air upon the under surface of the sintered sheet.

The above brief description, `as well as further objects, features and advantages of the present invention will be best understood by reference to the following detailed description of a presently preferred process and illustrative apparatus, when taken in conjunction with the accornp anying drawing, wherein:

The single figure is an elevational view, with parts lbroken away and sectioned for clarity, of illustrative apparatus for continuously processing non-compacted powdered metal into sintered sheets in accordance with the present invention.

Referring now specifically to the drawing, there is shown a supply roller or spindle 10 which carries thereon a conveyor 12 of heat-destroyable, non-metallic material, such as a low ash residue paper. Among the cellulosic materials suitable for the conveyor is a double washed filter paper of the type manufactured by Schleicher and Schull Co., and Whatman Paper Co. The ash remaining in a 7 cm. double washed paper of Schleicher and Schull Co. weighs approximately .000006 gram; the ash residue in a 7 cm. double washed paper of lWhatman Paper Co. weighs approximately .00005 gram. Polystyrene films, such as manufactured under the trade marks Lustron and Styron are also suitable heat-destroyable conveyor materials. The conveyor, carrier or base 12, is trained over idler rollers 14, 16 and directed horizontally in the direction of the arrows along the feed plane P.

The conveyor 12 passes over a horizontally extending table or support 18 beneath the open mouth 20a of a feed hopper or bin 20 containing therein a mass of noncompacted metallic powder, designated generally by the letter M.

Following the support 18 and hopper 20, is a rolling mill 22 which includes rolls 24, 26 which cooperate in the feed plane P for compacting the metallic powder on the upper surface or run of the conveyor 12.

Following the rolling mill 22 is a heat treatment chamber 2.8 which includes an entry opening 28a and an exit opening 28b, both disposed in the feed plane P such that the assembly of the heat-destroyable conveyor 12 and the metallic material thereon may be passed through the ,chamber 28. A latitude of substitution is intended in the illustrative apparatus described aforesaid and many refinements and additions may be incorporated in a commercial installation. VFor example, a pre-tensioning system may be provided for the heat-destroyable conveyor 12 to assure a uniform feed rate along the feed plane P and relative to the hopper 20; the feed hopper 20 may be adjustable up and down with respect to the feed plane and/ or the size of the exit opening 20a adjusted such that varying quantities of material may be deposited on the conveyor 12 in a given time interval; the rollers 24, 26 may be adjustable toward and awayY from each other such that the spacing between the rollers may be accurately predetermined for rolling varying thicknesses-of sheet material; and the heat treatment chamber or furnace 28 may Vbe divided into various sections and provisions made for heat regulation such that the time and temperature of sintering may be accurately controlled.

In accordance with the present process, the conveyor 12 in its traverse beneath the mouth 20a of the hopper 20 receives thereon a uniformly spread, loose and uncompacted layer of metal powder. The layer of powder on the conveyor 12 is then moved through the-rolls 24, 26 of the mill 22 where the non-compacted powder is compressed and emerge as green, compact sheet.V Thisgreen, compact sheet is self-supporting and adheres to the underlying conveyor 12 and is advanced therewith into the heat treatment chamber 28 for sintering.

Sintering is accomplished in a hydrogen or nitrogen atmosphere; preferably provision is made in the chamber 28 for pre-heating, sintering and cooling of the sintered sheet. The heat in the sintering chamber 28 is'usually suicient to destroy the conveyor 12; however, if any residues of the conveyor Vstill adhere to the under surface of the sintered sheet, such residues may be readily detached by directing a blast of air against the undersurface of the sintered sheet, either in the cooling zone or externally of the chamber A28. Following the sintering, which causes the compacted particles to cohere into a continuous sheet, the sintered sheet may be subjected-to wellknown metallurgical processing, such as re-rolling and annealing, to increase strength and density. Such processing may be repeated in one or more passes depending upon the desired final characteristics of the sheet material. f Illustrative of the many applications to which the present process may be applied is the fabrication of sheets of nickel powder. Using a rolling mill having rolls of 2.75 inch diameter and a 4 inch face and a paper conveyor, nickel powder may be fed onto the conveyor at the open mouth of the hopper 20. Starting with carbonyl nickel of +100 mesh, a green compacted strip was attained having a thickness of .015 inch. The green, compacted strip was pre-sintered at 1000 C. in a hydrogen atmosphere for a period of approximately minutes and thereafter re-rolled. Without 4intermediate annealing, the pre-sintered sheet was again sintered in la hydrogen atmosphere and at a temperature of 1000 C. for a period of approximately 90 minutes. The resulting nickel sheet had a density of approximately 3.7 grams per cubic centimeter and a thickness of .0065 inch. When subjected to physical tests, the sheet was found to have good bending ductility.

Among the advantages realized in accordance with the present method is the ability to operate with the mill in the usual upright position and having a horizontal feed. Still further, the formation of the sintered sheet is compatible with subsequent processing by conventional metallurgy techniques. The use of a non-metallic heatdestroyable conveyor carrying the powder to the rolling mill is exceptionally convenient, in that the requisite support is provided without the problems of adherence or alloying of the powdered mass to the conveyor.

Numerous modifications and substitutions in the presy ent process may occur to those skilled in the art, and

accordingly the appended claims should be given a latitude of interpretation consistent with the disclosure; at times certain features of the invention will be used without a corresponding use of other features.

What I claim is:

l. In the manufacture of a metallic sheet from metal powder, the steps including uniformly spreading a loose non-compacted layer of metal powder onto a horizontally movable sheet of a material which will be destroyed at temperatures which cause said metal to sinter and having rigidity and strength sucient to support said non-compacted layer, compacting said layer whereby a composite of said layer and sheet is continuouslyformed which i composite is self-sustaining, horizontally passing said composite through a heat-treatment apparatus to cause said layer to sinter and to burn off said heat-destroyable sheet, and removing any residues of-said heat-destroyable sheet from the sintered layer.

2. In the manufacture of a metallic sheet from metal powder, the steps including uniformly spreading a loose non-compacted layer of metal powder onto a horizontally movable sheet of a material which will be destroyed at temperatures which cause said metal to sinter and having rigidity and strength sufficient to support said non-compacted layer, rolling said layer whereby a composite of said layer and sheet is continuously formed which cornposite is self-sustaining, and horizontally passing said composite through a heat-treatment apparatus to cause said layer to sinter and to burn said heat-destroyable sheet.

3. A method for producing sintered metal sheet from lpowder metal including the steps of uniformly spreading a loose and uncompacted powder metal in a layer onto a carrier which will be destroyed at temperatures which cause said powdered rnetal to sinter,V compacting said layer into a green sheet adhered to said carrier, heat treating said sheet to sinter the same and to substantially destroysaid carrier, and subjecting said sheet to further compacting andY annealing to increase the strength and density of said sheet.

vReferences Cited in the le of this patent UNITED STATES vPATENTS Naeser May 22, 1956 

1. IN THE MANUFACTURING OF A METALLIC SHEET FROM METAL POWER, THE STEP INCLUDING UNIFORMLY SPREADING A LOOSE NON-COMPACTED LAYER OF METAL POWDER ONTO A HORIZONTALLY MOVABLE SHEET OF A MATERIAL WHICH WILL BE DESTROYED AT TEMPERATURES WHICH CAUSE SAID METAL TO SINTER AND HAVING RIGIDITY AND STRENGTH SUFFICENT TO SUPPORT SAID NON-COMPACTED LAYER, AND SHEET ID CONTINOUSLY FORMED WHICH OF SAID LAYER AND SHEET IS CONTINOUSLY FORMED WHICH COMPOSITE IS SELF-SUSTAINING, HORIZONTALLY PASSING SAID COMPOSITE THROUGH A HEAT-TREATMENT APPARATUS TO CAUSE SAID LAYER TO SINTER AND TO BURN OFF SAID HEAT-DESTROYABLE SHEET, AND REMOVING ANY RESIDUES OF SAID HEAT-DESTROYABLE SHEET FROM THE SINTERED LAYER. 